空化水射流冲击强化2A12铝合金的性能分析及机理研究

发布时间：2018-03-16 17:07

本文选题：空化水射流　切入点：冲击强化　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：喷丸是一种常见的被用于提高金属材料表面性能及其疲劳寿命的表面处理工艺,而空化水射流喷丸技术作为一种新型的表面处理工艺,其利用材料表面附近空化泡溃灭瞬间释放的高压冲击反复作用于材料表面,使材料表层发生塑性形变,产生残余压应力场,提高表面硬度,而粗糙度值却不会明显增大,从而有效提高材料表面性能。同时,该工艺所具有的一系列独特优势,如绿色环保、通用性高以及易于实现自动化等,使其正日益成为表面处理技术领域中一个新的研究方向。本文以空化水射流技术为基础,以实现绿色高效的喷丸方式、提高金属材料表面性能为出发点,采用理论分析的方法,对空化水射流喷丸工艺中空化泡的运动与动力学基础、发展溃灭过程以及冲击强化机理进行了分析。采用FLUENT数值模拟方法,对所设计喷嘴(收缩型、角型和风琴管喷嘴)的空化性能进行分析。通过对喷嘴在高压水射流环境下的速度场、压力场以及气相体积分数分布进行对比分析后发现:作为一种空化喷嘴,收缩型喷嘴的空化效果最不理想,风琴管喷嘴在一定程度上能够满足空化生成的需要,但角型喷嘴的空化性能最为突出,其内外流场的空化泡群密度及分布广度均要优于其他两种喷嘴,有利于空化水射流系统的稳定输出。同时,采用试验研究的方法,利用相关设备组装完成空化水射流喷丸装置,选取广泛应用于对零部件表面综合性能要求较高的航空、航天、汽车以及军工等领域中的2A12铝合金材料作为空化水射流喷丸试验的试样,检测并比较分析了不同喷丸工艺参数下材料表面的各项性能,得出本试验环境下的最佳喷丸工艺参数是入射压力P=20MPa,靶距S=40mm,喷丸时间T=4min。经过最佳喷丸工艺参数处理后的试样表面的硬度值约为137HV,较原始试样的表面硬度提高近48.9%;最大残余压应力及其深度则分别达到320MPa、390μm,相对于喷丸前的原始试样分别提升3.7倍、6.5倍;而表面粗糙度值只增加至1.29μm。并且通过观察试样表面的微观形貌,可以明显看到空化泡溃灭冲击影响区的凹凸形貌过渡区连贯平滑,并没有衍生出传统喷丸中常见的尖锐棱边、微裂纹等形变,避免了这些形变处的应力集中,对空化水射流喷丸强化下的金属材料表面性能够起到较好的增益效果。
[Abstract]:Shot peening is a common surface treatment process used to improve the surface properties and fatigue life of metal materials, while cavitation water jet peening is a new surface treatment technology. The high pressure impact released by cavitation bubble collapsing near the surface of the material repeatedly acts on the surface of the material, resulting in plastic deformation of the surface of the material, resulting in residual compressive stress field and increasing the surface hardness, but the roughness value does not increase obviously. At the same time, the process has a series of unique advantages, such as green environmental protection, high versatility and easy to realize automation, etc. Therefore, it is becoming a new research direction in the field of surface treatment technology. Based on cavitation water jet technology, in this paper, the method of theoretical analysis is adopted to realize green and efficient shot peening and to improve the surface properties of metal materials. The motion and dynamics basis of cavitation water jet shot peening process, the development of collapse process and the mechanism of impact strengthening are analyzed. The designed nozzle (shrinkage type) is simulated by FLUENT numerical simulation method. By comparing the velocity field, pressure field and gas phase volume fraction distribution of the nozzle under the high pressure water jet environment, it is found that the nozzle is a cavitation nozzle. The cavitation effect of constrictive nozzle is the least, the organ nozzle can meet the need of cavitation to some extent, but the cavitation performance of angle nozzle is the most outstanding. The density and distribution of cavitation bubble group in the internal and external flow field are superior to those of the other two kinds of nozzles, which is beneficial to the steady output of cavitation water jet system. At the same time, the cavitation water jet shot peening device is completed by means of experimental study and related equipment. The aluminum alloy 2A12, which is widely used in aviation, aerospace, automobile and military industry, which is widely used in the field of air, aerospace, automobile and military industry, is selected as the sample of cavitation water jet shot peening test. The properties of the material surface under different parameters of shot peening were tested and compared. It is concluded that the optimum parameters of shot peening in this test environment are incident pressure P0 20 MPA, target distance 40 mm, shot peening time T4 min. The hardness of the sample surface treated by the best shot peening parameters is about 137 HVV, which is 48.9% higher than that of the original sample. The maximum residual compressive stress and its depth are respectively 320MPA ~ (390) 渭 m, which are 3.7 times and 6.5 times higher than those of the original sample before shot peening. The surface roughness was only increased to 1.29 渭 m. By observing the microscopic morphology of the sample surface, it can be seen that the transition zone of the concave and convex morphology of the affected area of cavitation bubble collapsing is smooth, and there is no derivation of the sharp edge commonly seen in the traditional shot peening. The microcracks and other deformation can avoid the stress concentration at these deformations and can improve the surface properties of metal materials strengthened by cavitation water jet shot peening.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21;TG668

【参考文献】